Process for producing fullerene

ABSTRACT

A process for efficiently producing a target fullerene having a high purity in high yield by a simple method comprising simple steps using small amounts of a solvent and a reagent. The process for fullerene production comprises passing a solution obtained by dissolving a fullerene mixture containing a fullerene in an organic solvent through a layer of powdery activated carbon and then passing an organic solvent in which fullerene C 70  has a higher solubility than in that organic solvent. Thus, fullerene C 60  and fullerene C 70  can be separately obtained.

TECHNICAL FIELD

The present invention relates to an efficient process for preparingfullerene using activated carbon.

BACKGROUND ART

Fullerene is the generic name of fullerene C₆₀, in which 60 carbon atomsare bonded, and analogs thereof. Examples are fullerene C₆₀, which is asoccer ball-shaped molecule, and fullerene C₇₀, which is a rugbyball-shaped molecule, and as those having at most 100 carbon atoms, C₇₆,C₇₈, C₈₂, C₈₄, C₉₀ and C₉₆ are known.

Research on fullerenes is currently progressing worldwide. Applicationsof fullerenes to superconductors with high Tc, semiconductors,photoconductive composite materials, nonlinear optical materials,photoconductive materials, molecular ferromagnetic materials, solidlubricants and physiologically active substances have been reported, butare not yet realized. The greatest factor for this is said to lie incost of fullerenes and low-cost process for mass-production offullerenes with high purity is strongly desired so that fullerenes canbe widely used in society.

The above fullerenes are obtained by producing soot from raw materialsuch as graphite or hydrocarbon by laser ablation, arc discharge orcombustion and then purifying fullerene mixture extracted from the soot.As methods for purifying fullerene C₆₀, known are column chromatography,recrystallization, sublimation, extraction with supercritical fluid,selective inclusion and precipitation with calixarene and a methodutilizing solubility difference. However, although fullerene C₆₀ withhigh purity can be obtained, column chromatography, the method mostcommonly used at present, requires a large amount of both mobile andstationary phases and is time-consuming and also, there is the problemthat the amount that can be purified in one run is limited.

In order to solve these problems, selective inclusion and precipitationwith calixarene (JP-A-7-237911) and a method utilizing solubilitydifference (JP-A-7-10512) have been developed. According to thesemethods, although a relatively large amount can be purified in one run,complicated operation, such as repeating heating, stirring for a longtime and filtration several times, is necessary in order to obtainfullerenes with high purity of at least 99%, and furthermore, yield isnot very high. Also, C₇₀ with high purity cannot be obtained by eithermethod.

On the other hand, as a purification process for easily mass-producingfullerene C₆₀ with high purity, JP-A-5-85711 discloses the method ofextracting soot containing fullerene C₆₀ with an organic solvent such astoluene, adding powdered activated carbon to the extracted solution,stirring the mixture, separating and evaporating toluene to obtain apurified substance. Specifically, the above method is the method ofpurifying C₆₀ by adding activated carbon into an organic solution inwhich soot is dissolved, stirring the obtained suspension while heatingat 70° C. for 15 minutes to 2 hours, separating solid and liquid andthen concentrating the filtrate. The form and particle size of activatedcarbon used herein is not particularly limited. In this method,contacting with activated carbon is troublesome and requires time and,furthermore, yield is not very high. Also, purity is not mentioned. InExample 1, yield of fullerene C₆₀, which is obtained by dispersing 20 gof powdered activated carbon in a toluene solution, in which 5 g of sootcontaining fullerene C₆₀ is dissolved, and conducting operations such asfiltration after heating and stirring at 70° C. for 15 minutes, was 260mg. When considering that soot produced by arc discharge contains about10% of C₆₀, the yield is considered to be about 50%. Also, the amount ofpowdered activated carbon that is used is about 40 times the amount offullerene C₆₀ contained in soot and an extremely large amount ofactivated carbon is necessary. Example 2 describes that when the sameoperation was conducted using 5 g of powdered activated carbon andstirring for 2 hours, 160 mg of fullerene C₆₀ was obtained. In the sameway, the yield is presumed to be about 30%. By reducing the amount ofactivated carbon and increasing the stirring time, the yield issignificantly decreased. The reason therefor is not clear. However,according to this method, an extremely large amount of powderedactivated carbon based on fullerene C₆₀ is necessary and when the amountof powdered activated carbon is reduced, the treatment time becomeslonger and yield decreases. Furthermore, the method of passingfullerenes using activated carbon as a stationary phase is suggested,but the conditions thereof are not disclosed.

The present invention solves the above problems and relates to a processfor efficiently preparing fullerenes with high purity in high yields byfacile process and operation, and also a small amount of a solvent and areagent.

DISCLOSURE OF INVENTION

That is, the present invention relates to a process for preparingfullerene, which comprises passing a solution of a fullerene mixturethrough a layer of powdered activated carbon.

The fullerene is preferably fullerene C₆₀.

The layer of powdered activated carbon is preferably washed with anorganic solvent.

The fullerene is preferably fullerene C₇₀ and an organic solvent havinghigher solubility of fullerene C₇₀ than the above organic solvent ispreferably passed through the layer of powdered activated carbon,through which the solution is passed.

The organic solvent is preferably xylene.

The powdered activated carbon preferably has a particle size of at most50 mesh.

The amount of the powdered activated carbon is preferably 50 to 5000% byweight based on the fullerene mixture.

The thickness of the layer of powdered activated carbon is preferably 1to 150 mm.

The flow rate of the solvent per unit area of the layer of activatedcarbon is preferably 1.0 to 20 ml/minute·cm².

BEST MODE FOR CARRYING OUT THE INVENTION

In the process of the present invention, passing through a filter cakeof powdered activated carbon refers to conducting the step of filteringa fullerene solution, previously obtained by dissolving a fullerenemixture containing fullerenes in an organic solvent, by a filter layeron which powdered activated carbon is placed. Also, the step of passingan organic solvent through the filter cake can be included. Thereafter,fullerene is prepared by conducting the step of removing the organicsolvent from the obtained filtrate.

The fullerene mixture used in the present invention can be a substancecontaining fullerene C₆₀, fullerene C₆₀ and fullerene C₇₀, orderivatives and analogs thereof and the method for preparing thefullerene mixture is not particularly limited. An example is sootproduced from raw material such as graphite and hydrocarbon by laserablation, arc discharge or combustion. The fullerene mixture can also bethe extracted solution, which is obtained by extracting crude fullerenefrom soot by an organic solvent, or a substance commercially availableas, for example, powder of raw fullerene soot. Also, a mixture havinghigh fullerene C₆₀ content (70 to 75%) or relatively low content (60 to65%) can be used, as fullerene C₆₀ can be sufficiently separatedaccording to the present invention. Soot contains substances that areinsoluble in an organic solvent and when soot is added to an organicsolvent, a suspension is formed. This suspension can also be used as thesolution used in the present invention. Furthermore, the process of thepresent invention can also be used for preparing endohedralmetallofullerenes and heterofullerenes.

The raw material of the powdered activated carbon used in the presentinvention is not particularly limited and examples are wood, sawdust,palm kernel, lignin, cow bone, blood, lignite, brown coal, peat andcoal. These are carbonized and then activated to obtain powderedactivated carbon. The method for activating is not particularly limitedand examples are chemical and steam activation. Of these, coalchemically activated with zinc chloride is preferable, as the coal isconsidered to have large pore volume, large pore diameter and largespecific surface area. Also, using activated carbon in the form ofpowder is one of the features in the present invention. When theactivated carbon is in a form other than powder, such as particle,granulate or fiber, fullerenes having 70 and more carbon atoms are notproperly retained by the activated carbon and poorly separated fromfullerene C₆₀. The particle size of the powdered activated carbon ispreferably at most 50 mesh by an ASTM sieve, that is smaller than about300 μm. When the particle size of activated carbon is more than 50 mesh(about 300 μm), retention of fullerenes of C₇₀ and more is weak,separation becomes poor and purity of fullerene C₆₀ tends to decrease.The particle size is more preferably 50 to 400 mesh (about 300 to 40μm), particularly preferably 100 to 400 mesh (about 150 to 40 μm),further preferably 100 to 330 mesh (about 150 to 50 μm), most preferably100 to 200 mesh (about 150 to 74 μm). When the particle size is smallerthan 400 mesh (about 40 μm), retention of not only fullerene C₇₀ butalso fullerene C₆₀ becomes strong, yield of fullerene C₆₀ decreases andseparation tends to take a long time. Also, the average particle size ispreferably 5 to 100 μm, more preferably 20 to 70 μm. The activatedcarbon can be used alone or at least two types of different particlesize, preparation process or raw material can be used in combination.The powdered activated carbon can also be used in combination with asubstance having molecular sieving ability or molecular adsorptionability such as adsorption resin, chelate resin, silica gel, alumina andmolecular sieves. The pore diameter in the activated carbon ispreferably 0.5 to 30 nm, more preferably 1 to 10 nm, particularlypreferably 2.5 to 5 nm. When the average pore diameter is less than 0.5nm, fullerenes of C₇₀ and more are hard to be adsorbed in the activatedcarbon and purity of fullerene C₆₀ tends to decrease. When the averagepore diameter is more than 30 nm, discrimination to fullerene C₆₀decreases and purity of fullerene C₆₀ tends to decrease. The activatedcarbon is more preferable the larger the specific surface area is, fromthe viewpoint that the amount of the activated carbon can be small. Thespecific surface area is preferably 500 to 4000 m²/g, from theviewpoints that fullerenes having 70 and more carbon atoms and otherimpurities can be properly retained to the activated carbon.

The layer of powdered activated carbon used in the present invention isobtained, for example, by placing powdered activated carbon on filterpaper. An example of the method therefor is the method of suspending thepowdered activated carbon in an organic solvent and filtering thesuspension with suction using a funnel, on which filter paper is laid,to evenly place the activated carbon on the filter paper. Besidessuction, activated carbon can be evenly placed under pressure or underatmospheric pressure. Also, a layer of powdered activated carbon ofvarious forms can be used, such as activated carbon paper in the form ofa sheet or a pleat and powdered activated carbon molded into a honeycombshape, a block or a cylinder. The powdered activated carbon ispreferably placed in an amount of 50 to 5000% by weight, more preferably400 to 1200% by weight, based on the fullerene mixture to be filtered.When the amount of activated carbon is less than 50% by weight,separation of fullerenes becomes poor and purity of fullerene C₆₀ tendsto decrease. When the amount is more than 5000%, yield of fullerene C₆₀tends to decrease or a large amount of solvent tends to becomenecessary.

The thickness of the layer of powdered activated carbon is preferably 1to 150 mm, more preferably 2 to 50 mm, further preferably 3 to 30 mm.When the layer is thinner than 1 mm, separating ability tends to becomepoor and when the layer is thicker than 150 mm, filtration tends to taketime.

Examples of the organic solvent that dissolves the fullerene mixture arebenzene, toluene, xylene, trimethylbenzene, chlorobenzene,dichlorobenzene, trichlorobenzene, bromobenzene, dibromobenzene,anisole, carbon disulfide, trichloroethylene, tetrachloroethylene andtetrachloroethane. These can be used alone or in a combination of two ormore kinds. Of these, toluene is preferable in that cost is low, theboiling point is not very high and fullerenes are suitably dissolved.

The concentration of the obtained fullerene solution depends on thesolvent that is used. For example, in the case of a toluene solution,the concentration is preferably 1 to 5 g/l. When the concentration ofthe solution is less than 1 g/l or more than 5 g/l, separation fromfullerenes of C₇₀ and more tends to become poor.

By filtering the fullerene solution using the layer of powderedactivated carbon, impurities other than fullerenes and fullerenes of C₇₀and more that are contained in the fullerene mixture before filtrationare adsorbed by the activated carbon and fullerene C₆₀ with high purityis contained in the filtrate. In order to increase the yield offullerene C₆₀, an organic solvent capable of dissolving fullerene C₆₀ ispreferably additionally passed through the layer of powdered activatedcarbon.

The flow rate (ml/minute·cm²) of the solvent per unit area (1 squarecentimeter) is preferably 1.0 to 20 ml/minute·cm², more preferably 1.5to 10 ml/minute·cm². When the rate is slower than 1.0 ml/minute·cm²,filtration takes a long time and when the rate is faster than 20ml/minute·cm², separating ability tends to become poor.

Furthermore, by successively using an organic solvent having highersolubility of fullerene C₇₀ than the above organic solvent, for example,in the case of fullerene C₆₀ and fullerene C₇₀ are contained in thefullerene mixture, both can be isolated to obtain fullerene C₆₀ andfullerene C₇₀ with high purity.

Examples of the organic solvent that is additionally passed through thelayer of powdered activated carbon in order to obtain fullerene C₆₀ in ahigh yield are toluene, benzene, trichloroethylene andtetrachloroethylene. Of these, toluene is preferable in that cost islow, the boiling point is not very high and fullerenes are suitablydissolved.

Examples of the organic solvent having higher solubility of fullereneC₇₀ than the above organic solvent that is passed through to obtainfullerene C₇₀ are xylene, trimethylbenzene, bromobenzene,dibromobenzene, anisole, chlorobenzene, dichlorobenzene,trichlorobenzene, carbon disulfide and tetrachloroethane. An organicsolvent having solubility of fullerene C₇₀ of more than 5.0 g/l at roomtemperature is preferable. Of these, from the viewpoint that fullerenesare easily dissolved, o-dichlorobenzene and xylene (o-xylene, m-xylene,p-xylene or mixtures thereof) are preferable. The solubility offullerene C₇₀ to o-dichlorobenzene and o-xylene are 36.2 g/l and 13.6g/l respectively. o-Xylene is most preferable from the viewpoints thato-xylene exhibits suitable solubility to fullerenes and can be easilyevaporated using a rotary evaporator in the same manner as toluene.

For example, in the filtrate obtained by filtering a fullerene mixturecontaining fullerene C₆₀ and fullerene C₇₀ dissolved in toluene by thelayer of powdered activated carbon and then passing toluene through,fullerene C₆₀ with high purity is contained. Then, by evaporatingtoluene, fullerene C₆₀ is obtained in a high yield. Herein, the value(1/g) obtained by dividing the volume of filtrate containing fullereneC₆₀ (1) by the amount of the fullerene mixture (g) is a standard of theamount of toluene that is necessary for obtaining fullerene C₆₀ and thevalue is preferably 0.3 to 2.0, more preferably 0.5 to 1.6. When thevalue is less than 0.3, yield of fullerene C₆₀ is low and when the valueis more than 2.0, concentration takes a long time.

Subsequently, by passing toluene through the layer of powdered activatedcarbon, a solution of fullerene C₆₀/fullerene C₇₀=3/7 to 2/8 isobtained. Herein, the value (1/g) obtained by dividing the volume offiltrate (1) by the amount of the fullerene mixture (g) is preferably0.7 to 1.5, more preferably 0.9 to 1.3. When the value is less than 0.7,the purity of fullerene C₇₀ obtained in a later fraction tends to becomelow and when the value is more than 1.5, yield of fullerene C₇₀ tends tobecome low.

Subsequently, by pouring o-xylene, fullerene C₇₀ can be obtained withhigh purity of 95% and more in a good yield. Herein, the value (1/g)obtained by dividing the volume of filtrate (1) by the amount of thefullerene mixture (g) is preferably 0.5 to 2.5, more preferably 1.0 to1.7. When the value is less than 0.5, yield of fullerene C₇₀ tends tobecome low and when the value is more than 1.5, concentration takes along time.

The process described below can be used as a specific process forpreparing fullerene. First, a toluene solution of a fullerene mixture ispassed through a layer containing powdered activated carbon. Then, bypassing toluene through the layer, a toluene solution of almostcompletely pure fullerene C₆₀ is obtained. By passing toluene throughthe above layer once more, a mixture of fullerene C₆₀ and fullerene C₇₀is obtained. The ratio of fullerene C₆₀ and fullerene C₇₀ in the toluenesolution is 3/7 to 2/8. Subsequently, by passing o-xylene through thelayer of activated carbon, fullerene C₇₀ can be obtained with highpurity of 95% and more in a good yield.

Another feature of the present invention is that the process of thepresent invention employs the extremely simple process of passing afullerene solution, obtained by dissolving a fullerene mixture in anorganic solvent, through a layer containing powdered activated carbon.Fullerenes with high purity can be obtained in a high yield byevaporating the solvent of the filtrate. That is, the process of thepresent invention can be applied to mass production, as the preparationprocess is extremely simplified and treatment is simple.

In this way, the process of the present invention can efficientlymass-produce fullerenes with high purity in a short period of time, bythe extremely simple process of merely passing a fullerene mixturesolution through a layer of powdered activated carbon, together with anorganic solvent.

EXAMPLE 1

About 150 ml of toluene was added to 12.0 g of powdered activated carbon(Tokusei Shirasagi™, 100 mesh, average particle size 56 μm, average porediameter 3.3 nm, specific surface area 1430 m²/g) available from TakedaChemical Industries, Ltd. and the mixture was thoroughly mixed to obtaina suspension of activated carbon. The suspension was filtered withsuction using a funnel having a 6.0 cm diameter (made by Kiriyama GlassWorks Co.), on which a filter paper (No. 704 available from NipponRikagaku Kikai Co., Ltd.) was placed, to obtain a filter cake (thickness15 mm) comprising powdered activated carbon evenly spread all over thefilter paper. 1.50 g of a fullerene mixture (containing 75% of fullereneC₆₀ and 21% of fullerene C₇₀ available from Honjo Chemical Corporation)was dissolved in 750 ml of toluene and the solution was filtered withsuction through the above filter cake. When purple-colored solutionstarted to elute, suction was stopped and the filtrate was removed.Then, suction filtration was restarted and toluene and the removedfiltrate were passed through the filter cake again to obtain apurple-colored filtrate (1500 ml). The amount of toluene passed throughin 1 minute per unit area was 2.2 ml/minute·cm² and the time requiredfor filtration was 24 minutes. From this filtrate, toluene wasevaporated using a rotary evaporator and the residue was dried in vacuoto obtain 1.07 g of fullerene C₆₀ (purity 99%, yield 95%).Identification of fullerene C₆₀ and determination of purity wereconducted by HPLC. The results are shown in Table 1. The recoveredtoluene was reused without purification.

EXAMPLE 2

The purple-colored filtrate (1800 ml) was obtained in the same manner asin Example 1, except that the amount of powdered activated carbon was15.1 g and the thickness of the activated carbon layer was 18 mm. Theamount of toluene passed through in 1 minute per unit area was 2.1ml/minute·cm² and the time required for filtration was 30 minutes. 1.06g of fullerene C₆₀ (purity 99%, yield 94%) was obtained from thisfiltrate in the same manner as in Example 1. Identification of fullereneC₆₀ and determination of purity were conducted by HPLC. The results areshown in Table 1.

EXAMPLE 3

The purple-colored filtrate (1800 ml) was obtained in the same manner asin Example 1, except that 15.0 g of powdered activated carbon (ShirasagiP, 100 mesh, average particle size 52 μm, average pore diameter 2.4 nm,specific surface area 1020 m²/g) available from Takeda ChemicalIndustries, Ltd. was used and the thickness of the activated carbonlayer was 16 mm. The amount of toluene passed through in 1 minute perunit area was 2.1 ml/minute·cm² and the time required for filtration was30 minutes. 0.95 g of fullerene C₆₀ (purity 99%, yield 84%) was obtainedfrom this filtrate in the same manner as in Example 1. Identification offullerene C₆₀ and determination of purity were conducted by HPLC. Theresults are shown in Table 1.

EXAMPLE 4

About 30 ml of toluene was added to 5.0 g of powdered activated carbon(Darco G-60, 100 mesh, specific surface area 600 m²/g) available fromAmerican Norit Co. and the mixture was thoroughly mixed to obtain asuspension of activated carbon. The suspension was filtered with suctionusing a funnel having a 4.0 cm diameter (made by Kiriyama Glass WorksCo.), on which a filter paper (No. 5C available from Kiriyama GlassWorks Co.) was placed, to obtain a filter cake (thickness 10 mm)comprising powdered activated carbon evenly spread all over the filterpaper. 0.50 g of a fullerene mixture (containing 70% of fullerene C₆₀and 24% of fullerene C₇₀ available from Tokyo Kasei Kogyo Co., Ltd.) wasdissolved in 250 ml of toluene and the solution was filtered withsuction through the above filter cake. Subsequently, 400 ml of toluenewas passed through to obtain a purple-colored filtrate (650 ml). Theamount of toluene passed through in 1 minute per unit area was 2.6ml/minute·cm² and the time required for filtration was 20 minutes. Fromthis filtrate, toluene was evaporated using a rotary evaporator and theresidue was dried in vacuo to obtain 0.34 g of fullerene C₆₀ (purity99%, yield 97%). Then, after the previous toluene, 100 ml of a mixedsolution of toluene/o-dichlorobenzene=1/1 was passed through the filtercake under reduced pressure and subsequently 200 ml of o-dichlorobenzene(solubility of fullerene C₇₀ at room temperature 36.2 g/l (A. V.Eletskii, High Temperature, 34, 2, 303-318 (1996)) was passed through toobtain a reddish brown colored filtrate. From this filtrate,o-dichlorobenzene was evaporated by distillation under reduced pressureand the residue was dried in vacuo to obtain 0.072 g of fullerene C₇₀(purity 95%, yield 60%). Identification of fullerene C₆₀ and fullereneC₇₀ and determination of purity were conducted by HPLC. The results areshown in Table 1. The recovered toluene and o-dichlorobenzene werereused without purification.

EXAMPLE 5

About 80 ml of toluene was added to 18.0 g of powdered activated carbon(Darco G-60, 100 mesh, specific surface area 600 m²/g) available fromAmerican Norit Co. and the mixture was thoroughly mixed to obtain asuspension of activated carbon. The suspension was filtered with suctionusing a funnel having a 6.0 cm diameter (made by Kiriyama Glass WorksCo.), on which a filter paper (No. 704 available from Nippon RikagakuKikai Co., Ltd.) was placed, to obtain a filter cake (thickness 15 mm)comprising powdered activated carbon evenly spread all over the filterpaper. 1.50 g of a fullerene mixture (containing 75% of fullerene C₆₀and 21% of fullerene C₇₀ available from Honjo Chemical Corporation) wasdissolved in 750 ml of toluene and the solution was filtered withsuction through the above filter cake. Subsequently, 1450 ml of toluenewas passed through to obtain a purple-colored filtrate (2200 ml). Theamount of toluene passed through in 1 minute per unit area was 2.6ml/minute·cm² and the time required for filtration was 30 minutes. Fromthis filtrate, toluene was evaporated using a rotary evaporator and theresidue was dried in vacuo to obtain 1.08 g of fullerene C₆₀ (purity99%, yield 96%). Then, after the previous toluene, 300 ml of a mixedsolution of toluene/o-dichlorobenzene=1/1 was passed through the filtercake under reduced pressure and subsequently 1000 ml ofo-dichlorobenzene was passed through to obtain a reddish brown coloredfiltrate. From this filtrate, o-dichlorobenzene was evaporated bydistillation under reduced pressure and the residue was dried in vacuoto obtain 0.19 g of fullerene C₇₀ (purity 90%, yield 62%).Identification of fullerene C₆₀ and fullerene C₇₀ and determination ofpurity were conducted by HPLC. The results are shown in Table 1.

EXAMPLE 6

The purple-colored filtrate (1800 ml) was obtained in the same manner asin Example 5, except that the amount of toluene passed subsequently was1050 ml. The amount of toluene passed through in 1 minute per unit areawas 2.6 ml/minute·cm² and the time required for filtration was 25minutes. 1.04 g of fullerene C₆₀ (purity 99%, yield 92%) was obtainedfrom this filtrate in the same manner as in Example 5. Identification offullerene C₆₀ and determination of purity were conducted by HPLC. Theresults are shown in Table 1.

EXAMPLE 7

About 80 ml of toluene was added to 15.0 g of powdered activated carbon(Darco G-60, 100 mesh, specific surface area 600 m²/g) available fromAmerican Norit Co. and the mixture was thoroughly mixed to obtain asuspension of activated carbon. The suspension was filtered with suctionusing a funnel having a 6.0 cm diameter (made by Kiriyama Glass WorksCo.), on which a filter paper (No. 704 available from Nippon RikagakuKikai Co., Ltd.) was placed, to obtain a filter cake (thickness 13 mm)comprising powdered activated carbon evenly spread all over the filterpaper. 1.50 g of a fullerene mixture (containing 75% of fullerene C₆₀and 21% of fullerene C₇₀ available from Honjo Chemical Corporation) wasdissolved in 750 ml of toluene and the solution was filtered withsuction through the above filter cake. Subsequently, 1250 ml of toluenewas passed through to obtain a purple-colored filtrate (2000 ml). Theamount of toluene passed through in 1 minute per unit area was 2.8ml/minute·cm² and the time required for filtration was 25 minutes. Fromthis filtrate, toluene was evaporated using a rotary evaporator and theresidue was dried in vacuo to obtain 0.97 g of fullerene C₆₀ (purity99%, yield 86%). Then, after the previous toluene, 800 ml ofchlorobenzene was passed through the filter cake under reduced pressureand subsequently 1000 ml of o-dichlorobenzene was passed through toobtain a reddish brown colored filtrate. From this filtrate,o-dichlorobenzene was evaporated by distillation under reduced pressureand the residue was dried in vacuo to obtain 0.18 g of fullerene C₇₀(purity 90%, yield 55%). Identification of fullerene C₆₀, identificationof fullerene C₇₀ and determination of purity were conducted by HPLC. Theresults are shown in Table 1. The recovered toluene was reused withoutpurification.

EXAMPLE 8

The purple-colored filtrate (850 ml) was obtained in the same manner asin Example 5, except that 13.0 g of powdered activated carbon (PW-P, 100mesh) available from Kuraray Chemical Co., Ltd. was used and thethickness of the activated carbon layer was 9 mm. The amount of toluenepassed through in 1 minute per unit area was 3.0 ml/minute·cm² and thetime required for filtration was 10 minutes. 0.97 g of fullerene C₆₀(purity 96%, yield 86%) was obtained from this filtrate in the samemanner as in Example 5. Identification of fullerene C₆₀ anddetermination of purity were conducted by HPLC. The results are shown inTable 1.

EXAMPLE 9

About 30 ml of toluene was added to 5.1 g of powdered activated carbon(No. 102186, 150 mesh, average particle size 30 μm) available from Merck& Co., Inc. and the mixture was thoroughly mixed to obtain a suspensionof activated carbon. The suspension was filtered with suction using afunnel having a 4.0 cm diameter (made by Kiriyama Glass Works Co.), onwhich a filter paper (No. 5C available from Kiriyama Glass Works Co.)was placed, to obtain a filter cake (thickness 10 mm) comprisingpowdered activated carbon evenly spread all over the filter paper. 0.48g of a fullerene mixture (containing 73% of fullerene C₆₀ and 24% offullerene C₇₀ available from Tokyo Kasei Kogyo Co., Ltd.) was dissolvedin 300 ml of toluene and the solution was filtered with suction throughthe above filter cake. Subsequently, 130 ml of toluene was passedthrough to obtain a purple-colored filtrate (430 ml). The amount oftoluene passed through in 1 minute per unit area was 2.9 ml/minute·cm²and the time required for filtration was 12 minutes. From this filtrate,toluene was evaporated using a rotary evaporator and the residue wasdried in vacuo to obtain 0.32 g of fullerene C₆₀ (purity 99%, yield91%). Identification of fullerene C₆₀ and determination of purity wereconducted by HPLC. The results are shown in Table 1.

EXAMPLE 10

About 30 ml of toluene was added to 5.6 g of powdered activated carbon(No. 102186, 150 mesh, average particle size 30 μm) available from Merck& Co., Inc. and the mixture was thoroughly mixed to obtain a suspensionof activated carbon. The suspension was filtered with suction using afunnel having a 4.0 cm diameter (made by Kiriyama Glass Works Co.), onwhich a filter paper (No. 5C available from Kiriyama Glass Works Co.)was placed, to obtain a filter cake (thickness 11 mm) comprisingpowdered activated carbon evenly spread all over the filter paper. 0.55g of a fullerene mixture (containing 73% of fullerene C₆₀ and 24% offullerene C₇₀ available from Tokyo Kasei Kogyo Co., Ltd.) was dissolvedin 250 ml of toluene and the solution was filtered with suction throughthe above filter cake. Subsequently, 160 ml of toluene was passedthrough to obtain a purple-colored filtrate (410 ml). The amount oftoluene passed through in 1 minute per unit area was 2.7 ml/minute·cm²and the time required for filtration was 12 minutes. From this filtrate,toluene was evaporated using a rotary evaporator and the residue wasdried in vacuo to obtain 0.37 g of fullerene C₆₀ (purity 99%, yield92%). Identification of fullerene C₆₀ and determination of purity wereconducted by HPLC. The results are shown in Table 1.

EXAMPLE 11

About 50 ml of toluene was added to 1.2 g of powdered activated carbon(Tokusei Shirasagi™, 100 mesh, average particle size 56 μm, average porediameter 3.3 nm, specific surface area 1430 m²/g) available from TakedaChemical Industries, Ltd. and the mixture was thoroughly mixed to obtaina suspension of activated carbon. The suspension was filtered withsuction using a funnel having a 2.1 cm diameter (made by Kiriyama GlassWorks Co.), on which a filter paper (No. 5C available from KiriyamaGlass Works Co.) was placed, to obtain a filter cake (thickness 10 mm)comprising powdered activated carbon evenly spread all over the filterpaper. 148 mg of a fullerene mixture (containing 59% of fullerene C₆₀and 31% of fullerene C₇₀ available from MTR Ltd.) was dissolved in 50 mlof toluene and the solution was filtered under reduced pressure by theabove filter cake. When purple-colored solution started to elute,suction was stopped and the filtrate was removed. Then, suctionfiltration was restarted and subsequent to the toluene solution of thefullerene mixture, toluene containing the removed filtrate was passedthrough the filter cake again until reddish components started flowingout to obtain a purple-colored filtrate (about 100 ml). The amount oftoluene passed through in 1 minute per unit area was 6.4 ml/minute·cm²and the time required for filtration was 5 minutes. From this filtrate,toluene was evaporated using a rotary evaporator and the residue wasdried in vacuo to obtain 75.7 mg of fullerene C₆₀ (purity 99%, yield87%).

Subsequently, 50 ml of toluene was poured. Then, toluene was evaporatedfrom the filtrate using a rotary evaporator and the residue was dried invacuo to obtain 12.3 mg of a mixture of fullerene C₆₀ and fullerene C₇₀(fullerene C₆₀/fullerene C₇₀=63/37). The ratio of fullerene C₆₀ andfullerene C₇₀ was approximately the same as that of the fullerenemixture before filtration and so the mixture can be returned to thefullerene mixture before filtration and used again for purification.

Thereafter, 200 ml of o-xylene was passed through the filter cake and afiltrate was obtained. o-Xylene was evaporated from this filtrate usinga rotary evaporator and the residue was dried in vacuo to obtain 47.0 mgof fullerene C₇₀ (purity 88%).

The following filtration was conducted in order to increase the purityof the fullerene C₇₀.

About 50 ml of toluene was added to 1.2 g of powdered activated carbon(Tokusei Shirasagi™, 100 mesh, average particle size 56 μm, average porediameter 3.3 nm, specific surface area 1430 m²/g) available from TakedaChemical Industries, Ltd. and the mixture was thoroughly mixed to obtaina suspension of activated carbon. The suspension was filtered withsuction using a funnel having a 2.1 cm diameter (made by Kiriyama GlassWorks Co.), on which a filter paper (No. 5C available from KiriyamaGlass Works Co.) was placed, to obtain a filter cake (thickness 10 mm)comprising powdered activated carbon evenly spread all over the filterpaper. 47.0 mg of the fullerene C₇₀ having purity of 88% obtained abovewas dissolved in 25 ml of toluene and the solution was filtered underreduced pressure by the above filter cake. Subsequently, 175 ml oftoluene was poured. After the receptacle was exchanged, 150 ml ofo-xylene was passed through and a filtrate was obtained. This filtratewas concentrated and dried in vacuo to obtain 21.5 mg of fullerene C₇₀(97%) at yield of 47% based on the fullerene C₇₀ in the originalfullerene mixture. Identification of fullerene C₆₀, identification offullerene C₇₀ and determination of purity were conducted by HPLC. Theresults are shown in Table 1.

EXAMPLE 12

71.1 mg of fullerene C₆₀ (purity 99%, yield 77%) was obtained in thesame manner as in Example 11, except that 149 mg of a fullerene mixture(containing 62% of fullerene C₆₀ and 30% of fullerene C₇₀ available fromMTR Ltd.) was used. The amount of toluene passed through in 1 minute perunit area was 6.4 ml/minute·cm² and the time required for filtration was5 minutes.

Subsequently, 50 ml of toluene was poured. 9.6 mg of a mixture offullerene C₆₀ and fullerene C₇₀ (fullerene C₆₀/fullerene C₇₀=66/34) wasobtained from this filtrate in the same manner as in Example 11. Theratio of fullerene C₆₀ and fullerene C₇₀ was approximately the same asthat of the fullerene mixture before filtration and so the mixture canbe returned to the fullerene mixture before filtration and used againfor purification.

Thereafter, 200 ml of o-xylene was passed through the filter cake and50.3 mg of fullerene C₇₀ (purity 88%) was obtained in the same manner asin Example 11.

In the same manner as in Example 11, in order to increase the purity ofthe fullerene C₇₀, 50.3 mg of the fullerene C₇₀ having purity of 88%obtained above was dissolved in 25 ml of toluene and the solution wasfiltered under reduced pressure by the filter cake on which 0.51 g ofactivated carbon was spread. Subsequently, 50 ml of toluene was passedthrough. After the receptacle was exchanged, 100 ml of O-xylene waspassed through and a filtrate was obtained. This filtrate wasconcentrated and dried in vacuo to obtain 20.9 mg of fullerene C₇₀(purity 98%) at yield of 46% based on the fullerene C₇₀ in the originalfullerene mixture. Identification of fullerene C₆₀, identification offullerene C₇₀ and determination of purity were conducted by HPLC. Theresults are shown in Table 1.

EXAMPLE 13

76.5 mg of fullerene C₆₀ (purity 99%, yield 86%) was obtained in thesame manner as in Example 11, except that 1.2 g of powdered activatedcarbon (Taiko S, 100 mesh, average particle size 35 μm, specific surfacearea 1250 m²/g) available from Futamura Chemical Industries Co., Ltd.was used as the powdered activated carbon, the thickness of theactivated carbon layer was 10 mm and 151 mg of a fullerene mixture wasused. The amount of toluene passed through in 1 minute per unit area was6.8 ml/minute·cm² and the time required for filtration was 7 minutes.

Subsequently, 50 ml of toluene was poured. 8.0 mg of a mixture offullerene C₆₀ and fullerene C₇₀ (fullerene C₆₀/fullerene C₇₀=81/19) wasobtained from this filtrate in the same manner as in Example 11. Theratio of fullerene C₆₀ and fullerene C₇₀ was approximately the same asthat of the fullerene mixture before filtration and so the mixture canbe returned to the fullerene mixture before filtration and used againfor purification.

Thereafter, 200 ml of o-xylene was passed through the filter cake and46.8 mg of fullerene C₇₀ (purity 91%, yield 91%) was obtained in thesame manner as in Example 11.

Identification of fullerene C₆₀, identification of fullerene C₇₀ anddetermination of purity were conducted by HPLC. The results are shown inTable 1.

EXAMPLE 14

82.6 mg of fullerene C₆₀ (purity 99%, yield 85%) was obtained in thesame manner as in Example 11, except that 1.2 g of powdered activatedcarbon (Taiko FC, 100 mesh, average particle size 45 μm, specificsurface area 1250 m²/g) available from Futamura Chemical Industries Co.,Ltd. was used as the powdered activated carbon, the thickness of theactivated carbon layer was 12 mm and 151 mg of a fullerene mixture(containing 64% of fullerene C₆₀ and 28% of fullerene C₇₀ available fromMTR Ltd.) was used. The amount of toluene passed through in 1 minute perunit area was 7.4 ml/minute·cm² and the time required for filtration was6 minutes.

Subsequently, 50 ml of toluene was poured. 10.7 mg of a mixture offullerene C₆₀ and fullerene C₇₀ (fullerene C₆₀/fullerene C₇₀=91/9) wasobtained from this filtrate in the same manner as in Example 11.

Thereafter, 200 ml of o-xylene was passed through the filter cake and41.2 mg of fullerene C₇₀ (purity 83%, yield 80%) was obtained in thesame manner as in Example 11.

Identification of fullerene C₆₀, identification of fullerene C₇₀ anddetermination of purity were conducted by HPLC. The results are shown inTable 1.

EXAMPLE 15

83.0 mg of fullerene C₆₀ (purity 99%, yield 84%) was obtained in thesame manner as in Example 11, except that 1.2 g of powdered activatedcarbon (Taiko KA, 100 mesh, average particle size 30 μm, specificsurface area 1180 m²/g) available from Futamura Chemical Industries Co.,Ltd. was used as the powdered activated carbon, the thickness of theactivated carbon layer was 9 mm and 150 mg of a fullerene mixture(containing 61% of fullerene C₆₀ and 33% of fullerene C₇₀ available fromMTR Ltd.) was used. The amount of toluene passed through in 1 minute perunit area was 7.3 ml/minute·cm² and the time required for filtration was5 minutes.

Subsequently, 200 ml of o-xylene was passed through the filter cake and33.5 mg of fullerene C₇₀ (purity 77%, yield 67%) was obtained in thesame manner as in Example 11.

Identification of fullerene C₆₀, identification of fullerene C₇₀ anddetermination of purity were conducted by HPLC. The results are shown inTable 1.

EXAMPLE 16

About 500 ml of toluene was added to 80 g of powdered activated carbon(Tokusei Shirasagi™, 100 mesh, average particle size 56 μm, average porediameter 3.3 nm, specific surface area 1430 m²/g) available from TakedaChemical Industries, Ltd. and the mixture was thoroughly mixed to obtaina suspension of activated carbon. The suspension was filtered withsuction using a funnel having a 15 cm diameter (nutsche), on which afilter paper (No. 2 available from ADVANTEC MFS, Inc.) was placed, toobtain a filter cake (thickness 17 mm) comprising powdered activatedcarbon evenly spread all over the filter paper. 9.1 g of a fullerenemixture (containing 69% of fullerene C₆₀ and 26% of fullerene C₇₀available from Honjo Chemical Corporation) was dissolved in 3000 ml oftoluene and the solution was filtered under reduced pressure by theabove filter cake. When purple-colored solution started to elute,suction was stopped and the filtrate (about 1700 ml) was removed. Then,suction filtration was restarted and subsequent to the toluene solutionof the fullerene mixture, toluene containing the removed filtrate waspassed through the filter cake again until reddish solution started toelute, to obtain a purple-colored filtrate (about 7000 ml). The amountof toluene passed through in 1 minute per unit area was 1.6ml/minute·cm² and the time required for filtration was 25 minutes. Fromthis filtrate, toluene was evaporated using a rotary evaporator and theresidue was dried in vacuo to obtain 6.0 g of fullerene C₆₀ (purity 98%,yield 95%).

Identification of fullerene C₆₀ and determination of purity wereconducted by HPLC. The results are shown in Table 1.

EXAMPLE 17

About 300 ml of toluene was added to 27 g of powdered activated carbon(Tokusei Shirasagi™, 100 mesh, average particle size 56 μm, average porediameter 3.3 nm, specific surface area 1430 m²/g) available from TakedaChemical Industries, Ltd. and the mixture was thoroughly mixed to obtaina suspension of activated carbon. The suspension was filtered withsuction using a funnel having a 9 cm diameter (made by Kiriyama GlassWorks Co.), on which a filter paper (No. 131 available from ADVANTECMFS, Inc.) was placed, to obtain a filter cake (thickness 13 mm)comprising powdered activated carbon evenly spread all over the filterpaper. 3.0 g of a fullerene mixture (containing 65% of fullerene C₆₀ and24% of fullerene C₇₀ available from Honjo Chemical Corporation) wasdissolved in 3000 ml of toluene and the solution was filtered underreduced pressure by the above filter cake. When purple-colored solutionstarted to elute, suction was stopped and the filtrate (about 600 ml)was removed. Then, suction filtration was restarted and subsequent tothe toluene solution of the fullerene mixture, toluene containing theremoved filtrate was passed through the filter cake again until reddishsolution started to elute, to obtain a purple-colored filtrate (about2200 ml). The amount of toluene passed through in 1 minute per unit areawas 1.7 ml/minute·cm² and the time required for filtration was 20minutes. From this filtrate, toluene was evaporated using a rotaryevaporator and the residue was dried in vacuo to obtain 1.8 g offullerene C₆₀ (purity 99%, yield 90%).

Identification of fullerene C₆₀ and determination of purity wereconducted by HPLC. The results are shown in Table 1.

EXAMPLE 18

About 50 ml of toluene was added to 1.5 g of powdered activated carbon(Tokusei Shirasagi™, 100 mesh, average particle size 56 μm, average porediameter 3.3 nm, specific surface area 1430 m²/g) available from TakedaChemical Industries, Ltd. and the mixture was thoroughly mixed to obtaina suspension of activated carbon. The suspension was filtered withsuction using a funnel having a 2.1 cm diameter (made by Kiriyama GlassWorks Co.), on which a filter paper (No. 5C available from KiriyamaGlass Works Co.) was placed, to obtain a filter cake (thickness 1.2 cm)comprising powdered activated carbon evenly spread all over the filterpaper. 150 mg of a fullerene mixture (containing 54% of fullerene C₆₀and 34% of fullerene C₇₀ available from Honjo Chemical Corporation) wasdissolved in 50 ml of toluene and the solution was filtered underreduced pressure by the above filter cake. Subsequent to the toluenesolution of the fullerene mixture, by pouring toluene at a rate of 18ml/minute until reddish components started to elute, a purple-coloredfiltrate (about 190 ml) was obtained. The amount of toluene passedthrough in 1 minute per unit area was 5.2 ml/minute·cm² and the timerequired for filtration was 11 minutes. From this filtrate, toluene wasevaporated using a rotary evaporator and the residue was dried in vacuoto obtain 75.5 mg of fullerene C₆₀ (purity 99%, yield 93%).

Subsequently, 150 ml of toluene was poured. Then, toluene was evaporatedfrom the filtrate using a rotary evaporator and the residue was dried invacuo to obtain 15.2 mg of a mixture of fullerene C₆₀ and fullerene C₇₀(fullerene C₆₀/fullerene C₇₀=31/69).

Thereafter, 200 ml of o-xylene was passed through the filter cake and23.7 mg of fullerene C₇₀ (purity 96%, yield 46%) was obtained byconcentrating the obtained filtrate using a rotary evaporator and vacuumdrying the residue. Identification of fullerene C₆₀, identification offullerene C₇₀ and determination of purity were conducted by HPLC. Theresults are shown in Table 1.

EXAMPLE 19

100 ml of toluene was added to 6.0 g of powdered activated carbon(Tokusei Shirasagi™, 100 mesh, average particle size 56 μm, average porediameter 3.3 nm, specific surface area 1430 m²/g) available from TakedaChemical Industries, Ltd. and the mixture was thoroughly mixed to obtaina suspension of activated carbon. The suspension was filtered withsuction using a funnel having a 4.0 cm diameter (made by Kiriyama GlassWorks Co.), on which a filter paper (No. 5C available from KiriyamaGlass Works Co.) was placed, to obtain a filter cake (thickness 1.4 cm)comprising powdered activated carbon evenly spread all over the filterpaper. 0.60 g of a fullerene mixture (containing 54% of fullerene C₆₀and 34% of fullerene C₇₀ available from Honjo Chemical Corporation) wasdissolved in 200 ml of toluene and the solution was filtered underreduced pressure by the above filter cake. Subsequent to the toluenesolution of the fullerene mixture, toluene was poured at a rate of 28ml/minute until reddish components started to elute to obtain apurple-colored filtrate (0.801). The amount of toluene passed through in1 minute per unit area was 2.2 ml/minute·cm² and the time required forfiltration was 29 minutes. From this filtrate, toluene was evaporatedusing a rotary evaporator and the residue was dried in vacuo to obtain0.28 g of fullerene C₆₀ (purity 99%, yield 88%).

Subsequently, 0.80 l of toluene was poured. Then, toluene was evaporatedfrom the filtrate using a rotary evaporator and the residue was dried invacuo to obtain 0.05 g of a fullerene mixture (fullerene C₆₀/fullereneC₇₀=19/81).

Thereafter, 200 ml of, 0.80 l of o-xylene was passed through the filtercake and 96.4 mg of fullerene C₇₀ (purity 96%, yield 48%) was obtainedby concentrating the obtained filtrate using a rotary evaporator andvacuum drying the residue. Identification of fullerene C₆₀,identification of fullerene C₇₀ and determination of purity wereconducted by HPLC. The results are shown in Table 1.

EXAMPLE 20

About 200 ml of toluene was added to 13.5 g of powdered activated carbon(Tokusei Shirasagi™, 100 mesh, average particle size 56 μm, average porediameter 3.3 nm, specific surface area 1430 m²/g) available from TakedaChemical Industries, Ltd. and the mixture was thoroughly mixed to obtaina suspension of activated carbon. The suspension was filtered withsuction using a funnel having a 6.0 cm diameter (made by Kiriyama GlassWorks Co.), on which a filter paper (No. 704 available from NipponRikagaku Kikai Co., Ltd.) was placed, to obtain a filter cake (thickness1.5 cm) comprising powdered activated carbon evenly spread all over thefilter paper. 1.35 g of a fullerene mixture (containing 54% of fullereneC₆₀ and 34% of fullerene C₇₀ available from MTR Ltd.) was dissolved in450 ml of toluene and the solution was filtered under reduced pressureby the above filter cake. Subsequent to the toluene solution of thefullerene mixture, toluene was poured at a rate of 60 ml/minute untilreddish components started to elute to obtain a purple-colored filtrate(1.65 l). The amount of toluene passed through in 1 minute per unit areawas 2.1 ml/minute·cm² and the time required for filtration was 27minutes. From this filtrate, toluene was evaporated using a rotaryevaporator and the residue was dried in vacuo to obtain 0.66 g offullerene C₆₀ (purity 99%, yield 90%).

Subsequently, 1.6 l of toluene was poured. Then, toluene was evaporatedfrom the filtrate using a rotary evaporator and the residue was dried invacuo to obtain 0.17 g of a fullerene mixture (fullerene C₆₀/fullereneC₇₀=28/72).

Thereafter, 200 ml of, 2.0 l of o-xylene was passed through the filtercake and 0.23 g of fullerene C₇₀ (purity 95%, yield 50%) was obtained byconcentrating the obtained filtrate using a rotary evaporator and vacuumdrying the residue. Identification of fullerene C₆₀, identification offullerene C₇₀ and determination of purity were conducted by HPLC. Theresults are shown in Table 1.

EXAMPLE 21

150 ml of toluene was added to 15.0 g of powdered activated carbon(Tokusei Shirasagi™, 100 mesh, average particle size 56 μm, average porediameter 3.3 nm, specific surface area 1430 m²/g) available from TakedaChemical Industries, Ltd. and the mixture was thoroughly mixed to obtaina suspension of activated carbon. The suspension was filtered withsuction using a Buchner funnel having a 7.0 cm diameter, on which afilter paper (No. 131 available from ADVANTEC MFS, Inc.) was placed, toobtain a filter cake (thickness 1.5 cm) comprising powdered activatedcarbon evenly spread all over the filter paper. 1.85 g of a fullerenemixture (containing 70% of fullerene C₆₀ and 23% of fullerene C₇₀available from Honjo Chemical Corporation) was dissolved in 400 ml oftoluene and the solution was filtered under reduced pressure by theabove filter cake. Subsequent to a toluene solution of the fullerenemixture, toluene (about 1 l) was poured at a rate of 0.18 l/minute untilreddish components started to elute, to obtain a purple-colored filtrate(about 1.4 l). The amount of toluene passed through in 1 minute per unitarea was 4.7 ml/minute·cm² and the time required for filtration was only8 minutes. From this filtrate, toluene was evaporated using a rotaryevaporator and the residue was dried in vacuo to obtain 1.20 g offullerene C₆₀ (purity 98%, yield 93%). Identification of fullerene C₆₀and determination of purity were conducted by HPLC. The results areshown in Table 1.

COMPARATIVE EXAMPLE 1

About 20 ml of toluene was added to 1.0 g of activated carbon (Darco, 20to 30 mesh, specific surface area 600 m²/g) available from AmericanNorit Co. and the mixture was thoroughly mixed to obtain a suspension ofactivated carbon. The suspension was filtered with suction using afunnel having a 2.1 cm diameter (made by Kiriyama Glass Works Co.), onwhich a filter paper (No. 5C available from Nippon Rikagaku Kikai Co.,Ltd.) was placed, to obtain a filter cake (thickness 15 mm) comprisingpowdered activated carbon evenly spread all over the filter paper. 49.7mg of a fullerene mixture (containing 75% of fullerene C₆₀ and 21% offullerene C₇₀ available from Honjo Chemical Corporation) was dissolvedin 25 ml of toluene and the solution was filtered with suction throughthe above filter cake. Subsequently, 25 ml of toluene was poured and areddish brown colored filtrate (50 ml) was obtained. As a result of HPLCanalysis, the filtrate was found to be a fullerene mixture containing78% of fullerene C₆₀ and 22% of fullerenes of a higher order of at leastfullerene C₇₀ and fullerene C₆₀ and fullerene C₇₀ could not be isolatedfrom each other. The results are shown in Table 2.

COMPARATIVE EXAMPLE 2

About 20 ml of toluene was added to 1.5 g of granulated activated carbon(made from palm shell, 30 to 60 mesh) available from Nacalai Tesque,Inc. and the mixture was thoroughly mixed to obtain a suspension ofactivated carbon. The suspension was filtered with suction using afunnel having a 2.1 cm diameter (made by Kiriyama Glass Works Co.), onwhich a filter paper (No. 5C available from Nippon Rikagaku Kikai Co.,Ltd.) was placed, to obtain a filter cake (thickness 18 mm) comprisingpowdered activated carbon evenly spread all over the filter paper. 50.4mg of a fullerene mixture (containing 73% of fullerene C₆₀ and 24% offullerene C₇₀ available from Tokyo Kasei Kogyo Co., Ltd.) was dissolvedin 25 ml of toluene and the solution was filtered with suction throughthe above filter cake. Subsequently, 25 ml of toluene was poured and areddish brown colored filtrate (50 ml) was obtained. As a result of HPLCanalysis, the filtrate was found to be a fullerene mixture containing76% of fullerene C₆₀ and 20% of fullerenes of a higher order of at leastfullerene C₇₀ and fullerene C₆₀ and fullerene C₇₀ could not be isolatedfrom each other. The results are shown in Table 2.

COMPARATIVE EXAMPLE 3

About 20 ml of toluene was added to 1.0 g of fibrous activated carbon(A-15, average pore diameter 2.1 mm, specific surface area 1670 m²/g)available from Unitika, Ltd. and the mixture was thoroughly mixed toobtain a suspension of activated carbon. The suspension was filteredwith suction using a funnel having a 2.1 cm diameter (made by KiriyamaGlass Works Co.), on which a filter paper (No. 5C available from NipponRikagaku Kikai Co., Ltd) was placed, to obtain a filter cake (thickness15 mm) comprising powdered activated carbon evenly spread all over thefilter paper. 50.8 mg of a fullerene mixture (containing 75% offullerene C₆₀ and 21% of fullerene C₇₀ available from Tokyo Kasei KogyoCo., Ltd.) was dissolved in 25 ml of toluene and the solution wasfiltered with suction through the above filter cake. Subsequently, 25 mlof toluene was poured and a reddish brown colored filtrate (25 ml) wasobtained. As a result of HPLC analysis, the filtrate was found to be afullerene mixture containing 76% of fullerene C₆₀ and 20% of fullerenesof a higher order of at least fullerene C₇₀ and fullerene C₆₀ andfullerene C₇₀ could not be isolated from each other. The results areshown in Table 2. TABLE 1 Thickness Toluene Solution of Activated CarbonUsed Diameter of Activated Fullerene Mixture Filtrate Particle Amount ofFunnel Carbon Layer Concentration Volume containing C₆₀ Yield of C₆₀ Ex.Size (Mesh) Used (g) (cm) (mm) (g/l) (ml) (ml) (%) 1 100 12.0 6 15 2 7501500 95 2 100 15.1 6 18 2 750 1800 94 3 100 15.0 6 16 2 750 1800 84 4100 5.0 4 10 2 250 650 97 5 100 18.0 6 15 2 750 2200 96 6 100 18.0 6 152 750 1800 92 7 100 15.0 6 13 2 750 2000 86 8 100 13.0 6 9 2 750 850 869 150 5.1 4 10 1.6 300 430 91 10 150 5.6 4 11 2.2 250 410 92 11 100 1.22.1 10 2.96 50 100 87 12 100 1.2 2.1 10 2.98 50 100 77 13 100 1.2 2.1 103.02 50 150 86 14 100 1.2 2.1 12 3.04 50 140 85 15 100 1.2 2.1 9 3 50114 84 16 100 80 15 17 3.03 3000 7000 95 17 100 27 9 13 1 3000 2200 9018 100 1.5 2.1 12 3 50 190 93 19 100 6.0 4 14 3 200 800 88 20 100 13.5 615 3 450 1650 90 21 100 15.0 7 15 4.625 400 1400 93

TABLE 2 Thickness Toluene Solution of Activated Carbon Used Diameter ofActivated Fullerene Mixture Filtrate Com. Particle Amount of FunnelCarbon Layer Concentration Volume containing C₆₀ Yield of C₆₀ Ex. Size(Mesh) Used (g) (cm) (mm) (g/l) (ml) (ml) (%) 1 20-40 1.0 2.1 15 2 25 50Mixture of (Particle) C₆₀ and C₇₀ 2 30-60 1.5 2.1 18 2 25 50 Mixture of(Particle) C₆₀ and C₇₀ 3 Fiber 1.0 2.1 15 2 25 25 Mixture of C₆₀ and C₇₀

INDUSTRIAL APPLICABILITY

According to the present invention, fullerenes with high purity can beefficiently prepared by the extremely simple process of merely passing afullerene compound through a layer of powdered activated carbon togetherwith an organic solvent. Also, the present invention is suited forproduction at an industrial level, since a large amount of fullerenescan be treated in a short period of time.

1. A process for preparing fullerene, which comprises passing a solutionof a fullerene mixture through a layer of powdered activated carbon. 2.The process of claim 1, wherein said fullerene is fullerene C₆₀.
 3. Theprocess of claim 1, which further comprises washing said layer ofpowdered activated carbon with an organic solvent.
 4. The process ofclaim 1, wherein said fullerene is fullerene C₇₀; and which furthercomprises passing an organic solvent having higher solubility offullerene C₇₀ than said organic solvent through said layer of powderedactivated carbon, through which said solution is passed.
 5. The processof claim 4, wherein said organic solvent is xylene.
 6. The process ofclaim 1, wherein said powdered activated carbon has a particle size ofat most 50 mesh.
 7. The process of claim 1, wherein the amount of saidpowdered activated carbon is 50 to 5000% by weight based on saidfullerene mixture.
 8. The process of claim 1, wherein the thickness ofsaid layer of powdered activated carbon is 1 to 150 mm.
 9. The processof claim 3, wherein the flow rate of said solvent per unit area of saidlayer of activated carbon is 1.0 to 20 ml/minute·cm².